1. Field of the Invention
The present invention relates to a vehicle steerable by movement of the center of gravity.
2. Description of Related Art
In a conventional method of steering a vehicle, such as an automobile or a motorcycle, a travel direction is controlled manually with a steering wheel or a handle bar and the vehicle speed is controlled by foot with a gas pedal or a brake pedal. Instead of such a conventional method of steering, steering by movement of the center of gravity is proposed, in which a position of the center of gravity on a steering step board on which a driver rides is detected and a vehicle is steered in association with the position of the center of gravity.
Japanese Patent Laid-Open Publication No. 2004-359094 (FIGS. 5 and 6) discloses such a vehicle steerable by movement of the center of gravity. The vehicle has a first drive motor, a second drive motor, a step board, a gravity center movement detector, and a drive controller. The first drive motor rotates and drives a left wheel. The second drive motor rotates and drives a right wheel. The step board is provided above a vehicle base to allow a person to ride thereon. The gravity center movement detector is provided between the vehicle base and the step board and detects movement of the driver's center of gravity. The drive controller drives and controls the first drive motor and the second drive motor based on a detection signal from the gravity center movement detector to enable straight travel and turning. The gravity center movement detector includes four pressure sensors assigned to respective corners of the step board. The drive controller drives and controls the left and right drive motors based on detection signals from the four pressure sensors. For example, when the center of gravity shifts forward from the center of the vehicle due to weight movement of the driver, the vehicle travels forward. When the center of gravity returns to the center of the vehicle, the left and right drive motors stop, and thus the vehicle stops. On the other hand, when the center of gravity shifts backward from the center of the vehicle, the vehicle travels backward.
Japanese Patent Laid-Open Publication No. 2004-138547 (FIGS. 1 and 2) discloses a drive control apparatus that controls a traveling driving source of a travel device based on load distribution of force exerted in association with driver's weight movement as driving operation of the travel device. During the control, an area where the load distribution is detected is divided into a plurality of sub-areas. The traveling driving source is controlled based on the distribution of load data detected in each sub-area. For instance, shifting the weight toward toes of both feet allows forward travel, while shifting the weight toward heels of the feet allows backward travel. Furthermore, shifting the weight toward the right foot allows a right turn, while shifting the weight toward the left foot allows a left turn. To stop, a state is generated where no load data of the feet are detected, specifically, the feet need to be brought down from a foot plate.
In the conventional technologies above, backward shifting of the center of gravity or backward shifting of the load position enables straight backward travel. In a case, however, where a driver rides while standing, the driver may be brought into such a position inadvertently. In order to prevent such inadvertent straight backward travel, the driver thus should have a sense of tension. In addition, the rotation speed of the left and right wheels, and thus the speed of the vehicle, is consequently determined by the position of the center of gravity or the load position of the driver in the conventional arts. Thus, traveling at a constant speed (cruising) is difficult. Accordingly, a vehicle is desired which is steerable by movement of the center of gravity to have less steering load on a driver.